1. Technical Field
The disclosure relates generally to micro electro-mechanical systems (MEMS), and more particularly, to methods of forming an oxide MEMS beam including a stress gradient.
2. Background Art
Micro Electro Mechanical Systems (MEMS) switches are fabricated such that there is a movable beam electrode which, when electrostatically actuated, makes contact to a second electrode. The second electrode is usually fixed to a surface under or over the movable beam electrode. The movable beam electrode, which can be a cantilever or bridge beam, is fabricated such that it is surrounded by a sacrificial material, such as silicon, oxide, or polymer which is subsequently removed to release the beam. MEMS switches are used, for example, for RF capacitors or contact switches, and range in thickness and length roughly from 0.1 m and 10 m to 10 m and 1000 m, respectively.
Other MEMS devices include resonators, acoustic wave devices, oscillators, motion detectors, pressure sensors, etc. which may have dielectric and semiconductor beams or beams formed of other materials. During wafer processing variation in film thickness or stress can induce undesirable MEMS beam bending. In addition, during operation, a MEMS beam bridge may be exposed to varying temperatures that causes the beam to bend up or down. This can affect the electrical properties of a wafer. Therefore, it is desirable to control the beam bending and to maintain a known beam stress. The stress of a thin film can be given in MPa and typical values for conductors, semiconductors, and dielectrics are normally in the range of −1000 MPa to 1000 Mpa and more typically in the range of −200 to 200 MPa. Negative stress means that the film is compressive; positive stress means that a film is tensile.